Significant progress in our understanding of the mechanisms of weight homeostasis has been made by studying the many genetic mouse models of obesity. Investigators into the molecular mechanisms that cause obesity in one of these models, like the lethal yellow moue, have led to the discovery of a novel neuropeptide receptor system that regulates food intake and metabolism. studies have shown that pro-opiomelanocortin neurons and the melanocortin 4 receptor play critical roles in regulation of weight homeostasis in the rodent. Although the significance of POMC neurons and the melanocortin 4 receptor in the rodent is apparent, the role of POMC neurons in the regulation of weight and feeding behavior in humans is currently unknown. Recent studies, however, suggest that differences in the POMC gene may indeed contribute the human obesity syndrome. Large scale studies of obese kindreds have linked the obese phenotype to the POMC locus in some families. Although specific mutations in the POMC coding region were not found in these kindreds, mutations in the POMC regulatory region remain possible. Since both peripheral pigmentation and pituitary adrenocorticotropin (ACTH) production appear to be normal in these families, a POMC regulatory region defect would most likely be found in enhance elements required for hypothalamic expression. On the basis of previous animal studies, decreases in hypothalamic POMC mRNA transcription are likely to lead to obesity in humans. A careful study of the role for hypothalamic POMC neurons in human obesity may help to explain a cause of the human obesity syndrome and lead to better methods of treatment. Therefore, the specific enhancer region using transgenic mice to test for specific expression of the human POMC transgene in mouse hypothalamus and in vitro methods to identify specific neural enhancer elements. 2) Test the POMC neuron specific enhance activity in obese human kindreds and identify specific POMC gene mutations. Hypothalamic POMC transcriptional activity from obese and non-obese individuals in this kindred will be investigated using the transgenic models. Sequence differences in the neuron specific enhancer region(s) in obese versus non obese individuals from this kindred will be defined. 3) Characterize the frequency and effect of human POMC neuron specific enhancer mutations in the general population. In addition, local families with POMC gene defects will be identified for use in clinical studies of the effect of POMC gene defects on weight homeostasis in humans.